1. Field of the Invention
The present invention relates generally to presses such as press brakes for bending sheet metals, and more particularly to a method and an apparatus for adjusting the stroke length of a ram for presses.
2. Description of the Prior Art
In presses, it is necessary to adjust the stroke length of a ram holding a tool or tools, according to materials and dimensions of workpieces to be formed or processed, dimensions and shapes to be made or formed on workpieces, and dimensions of tools to be used on presses. It is very difficult and time-consuming to adjust the stroke length of a ram in presses, since a slight error in setting the stroke length of a ram will cause bad finishes on workpieces to be formed or processed by the press.
Heretofore, various attempts have been made to adjust the stroke length of a ram in presses, but all of the conventional measures have suffered from serious shortcomings. For example, a micro switch means is used to define the stroking limit of a ram in presses, and such a micro switch means is adjusted to adjust the stroke length of the ram. In this case, when it is desired to change the tools of the press for other ones of different dimensions, it is necessary to accurately calculate the differences in the dimensions of the tools. In any of the conventional manners, it has been impossible to adjust the stroke length of a ram in presses by taking into account deflections which will be produced on presses in operations, and accordingly it has been necessary to determine the stroke length of a ram by trial and error by experimentally processing workpieces. Also, when it is desired to reuse worn tools after regrinding them, it is difficult and time-consuming to calculate the reduction in dimensions of the tools in order to determine the stroke length of the ram in the conventional manner. Also, it has been very difficult to correct the stroke length of a ram in a press in the conventional manner, when the frame of the press is subject to deflection because of a change in temperature. Such being the case, the stroke length of a ram in presses has been determined by trial and error by experimentally processing workpieces, and a number of workpieces are scrapped before an acceptable stroke length can be obtained.